Such a tensioning device is e. g. known from DE 4431161 A1. It is primarily employed for tensioning timing chains of a timing chain drive in an internal combustion engine. The tensioning piston presses onto a swiveling tensioning rail which is pressed against the timing chain. The tensioning device is connected to the engine oil hydraulics and is supplied, via an inflow with a check valve, with hydraulic oil which then flows into the pressure chamber. In this known device, the tensioning piston is designed as cylindrical hollow piston which comprises, at its front face, a vent opening in the form of a coaxially arranged vent hole. A vent disk is preceding the vent opening and provided with a meandering or spiral vent channel at its upper side. The vent disk comprises a slot at its circumference, so that air and hydraulic fluid can get from the pressure chamber into the vent channel. The other end of the vent channel flushes with the vent opening, so that air and hydraulic fluid can escape. The cross-section of the vent channel is normally smaller than the cross-section of the vent opening, resulting in a throttle effect that also has an influence on the damping behavior of the tensioning device. The vent channel is only formed in the vent disk in this known tensioning device. The bore shoulder in the tensioning piston only functions to seal the channel.
In another embodiment, the vent disk is an integral part of a packing element whose cylindrical extension projects into the interior of a pressure spring disposed in the pressure room and therefore reduces the total volume of the pressure room. This permits to more quickly fill the pressure room with hydraulic fluid during the starting operation of an internal combustion engine.
Further known tensioning devices are described in DE 4015708 C1, DE 202007008335 U1, and EP 1067275 A2.
It is a disadvantage of the known tensioning devices that only a certain area is available for the effective length of the throttle channel.